docs: def lighten(cmapin, alpha):
      '''Lighten a colormap by adding alpha < 1.
  
      :param cmap: A colormap object, like cmocean.cm.matter.
      :param alpha: An alpha or transparency value to assign the colormap. Alpha
          of 1 is opaque and of 1 is fully transparent.
  
      Outputs resultant colormap object.
  
      This will lighten the appearance of a plot you make using the output
          colormap object. It is also possible to lighten many plots in the
          plotting function itself (e.g. pcolormesh or contourf).
      '''
  
      # set the alpha value while retaining the number of rows in original cmap
      return cmap(cmapin(np.linspace(0,1,cmapin.N), alpha))